The Reuters news agency is being accused of publishing an altered photo in it’s editor’s choice blog. The remarkable photo shows a man firing a rocket-propelled grenade (RPG). It is being argued that the shadows in the photo are improbable because the shadows of the RPG launcher and the subsequent blast cannot be seen alongside the shadow of the man. In response to these accusations, Reuters withdrew the photo from their blog. We believe, however, that the shadows and lighting in this photo are physically plausible.
Welcome to the Fourandsix blog, where you’ll find tips on image forensics techniques and commentary on issues relevant to photo tampering and the responsible use of imaging tools.
As I described in two previous posts (“Enhance – no, really” and “Optical teleduplication”) Photoshop can be used to un-distort planar surfaces such as a license plate or the surface of a key. The intuition behind this is that planar surfaces are inherently two-dimensional and therefore no information is lost when they are imaged from a 3D world into a 2D image. Kevin recently pointed out to me that the same Photoshop tools that allow for these distortions to be removed can be used to measure the size of objects/people in an image.
Previously, I discussed why Adobe Camera Raw (ACR) is such a useful tool for photo editing workflows that need to be constrained to truthful representations. One of the key reasons why it is such a useful tool is that it lacks the sophisticated compositing and special effects features of the full Photoshop application, instead focusing primarily on tools that enhance rather than fundamentally change image content. Nevertheless, there are a few editing controls in ACR you may want to avoid, and even the most fundamental image enhancements, when pushed to their limits, can begin to mislead the viewer.
As I began to write part 2 of my Adobe Camera Raw overview, I realized that it would be helpful first to express some basic principles that I’ll be using in recommending the use of specific tools in a truthful photo editing workflow. Software like Adobe Photoshop presents a vast array of tools and functions. Each tool or function manipulates your image data in different ways, and the nature of this manipulation—as well as the context in which the image will be viewed—will impact the truthfulness of your results. As a starting point, however, I always ask myself two key questions:
For anyone who seeks to truthfully enhance a photograph without fundamentally changing the content it depicts, there are two characteristics that would be most valuable in a photo editing tool: 1) a collection of editing controls that omits those features that are primarily designed for artistic embellishment, and 2) an auditing trail that makes it easy to show anyone exactly how you got from the original captured image to the final enhanced version. Such a tool would limit the temptation of over-manipulating the photograph while also making it easy for a third party to verify the truthfulness and appropriateness of your edits. As it turns out, such an editing tool already exists inside the program that most professionals use, Adobe Photoshop. That editing tool is Adobe Camera Raw (ACR), and it deserves to be the first stop for anyone using Photoshop for photojournalism, image forensics, scientific imaging, and similar fields.